Add ice cubes and water to a measuring cup. Cut the butter into ¼" cubes. Place both items in the refrigerator until ready to use.

In a stand mixer bowl, add the flour and salt. Mix using the paddle attachment on the lowest speed for about 10 seconds. Add the chilled butter to the bowl.

Mix on low speed until the flour and butter resemble wet sand with pea-sized butter pieces remaining, about 60 to 70 seconds.

Gradually add water until the dough looks lumpy and hydrated but not wet or sticky.

Press the dough into a 1” thick round disc and wrap it in plastic, then place it in a resealable bag. Store in the refrigerator to rest for at least 4 hours.

Preheat the oven to 375°F (190°C). Remove the dough from the refrigerator and roll into a 14-inch circle.

Place the rolled-out dough into a 9-inch pie dish and gently press against the sides and bottom. Trim the excess.

Freeze the crust for 20 minutes, then place a piece of parchment paper inside and add pie weights. Bake for 20 minutes.

Remove the parchment and continue to bake until golden brown, about 10 to 15 minutes. Transfer to a wire rack to cool.

In a small bowl, whisk together sugar, cornstarch, cocoa powder, and salt.

In a medium bowl, whisk together eggs and add the cornstarch mixture.

Heat milk in a pot until it reaches 180 to 185ºF, then turn off the heat.

Temper the eggs with the hot milk mixture, then whisk the tempered eggs into the rest of the milk.

Cook over medium heat, whisking until thickened. Turn off heat and whisk in chocolate, butter, and vanilla.

Strain the custard into the pie shell and smooth it out. Cover with plastic wrap and chill for at least 3 hours.

Right before serving, make whipped cream by whipping cream with powdered sugar and vanilla until stiff peaks form.

Spread or pipe whipped cream over the pie and garnish with chocolate shavings if desired.

Refrigerate the pie until ready to serve.